DNA polymerases are widely used in in vitro applications. In particular, use of thermostable polymerases has revolutionized modern molecular biology. The processivity of a DNA polymerase, i.e., the length of product generated by the enzyme per binding event, is an important factor in many in vitro reactions. For example, in a PCR reaction or an in vitro sequence assembly reaction, the length of a product is largely determined by the proofreading activity and the processivity of the DNA polymerase used. Increasing the processivity of a DNA polymerase can, in theory, allow one to copy and/or amplify a template (particularly a longer template) more efficiently altering the fidelity of the polymerase. However, in practice, increasing the processivity of a DNA polymerase does not always have the desired effect because the proofreading activity of the polymerase may counteract any positive effects conferred by the increase in processivity.
One way to increase the processivity of a DNA polymerase involves adding Sso7d, a non-specific DNA binding protein, onto the polymerase (Wang et al, Nuc. Acids Res. 2004 32: 1197-1207). Because Sso7d binds DNA non-specifically, it is thought that the addition of the domain helps anchor the polymerase to its template, thereby stabilizing the interaction between the polymerase and the template.